The invention pertains to web feeding apparatus, and more particularly, to those wherein a controlled web loop is provided between adjacent roller stations. See, for example, U.S. Pat. Nos. 3,912,145; 3,807,613; 3,322,315; 3,680,753; 3,905,533; 3,587,959; and 3,326,436.
Typically, the web loop is provided together with a dancer member biased into engagement with the web loop to maintain tension therein. In order to maintain desired tension in the web loop, a rotary transducer means has been coupled to the dancer member to indicate whether the tension is too great or too little. The signal from the transducer has been employed to control the drive means of the web feeding system to ensure proper web tensioning. The prior art devices have typically employed a potentiometer or other electromechanical means as the rotary transducer. See, for example, U.S. Pat. Nos. 3,912,145; 3,807,613; 3,322,315; 3,680,753; and 3,905,533.
A problem with such electromechanical means is their susceptibility to wear and the generation of noise.
Other systems have attempted to synchronize the web flow speed at the various stations by employing electromechanical tachometer generators at such stations in order to determine the various station motor speeds to synchronize them. Wear and noise problems are also associated with these electromechanical devices. U.S. Pat. No. 3,452,853 shows the use of an electromechanical tachometer generator.
Still other systems have employed optical sensing means reading directly on the paper web in order to determine the speed thereof and control the same as necessary. The use of such optical sensing means requires the presence of reference marks on the paper web. See, for example, U.S. Pat. Nos. 3,326,436; 3,949,856; 3,323,700; 3,368,726; 4,025,025; and 4,047,085.
Where the system involved is a printer for serialized forms, typically a transfer station will transfer toner particles to the paper web followed by a fuser station which employs a combination of heat and pressure to fix the toner to the paper. It is often necessary, for various reasons, to stop the paper web during a run. A desirable feature of the printer is the ability to stop and start between adjacent forms without losing a form in sequence. Printing is conventionally not permitted in an area within one-half inch of the between-forms perforations. Consequently, the paper motion control system must cause the paper to accelerate and decelerate within one-half inch distance.
In addition, when the paper web is stopped at the fuser station, it is important that it be stopped at a between-forms perforation in the "nip" or interference area between the pressure roller and the heater roller. If this is not done, the toner on the paper will become overheated and smear.
During a paper stop cycle, the toner deposited on the web loop between the transfer station and fuser station is held to the paper by a decaying electrostatic force. If this paper loop is jarred or excessively accelerated at start-up, the toner may be displaced. Consequently, there is a need for a system which provides smooth and controlled acceleration and deceleration of the paper loop.
There is, therefore, a need for a web feeding system which accomplishes all the foregoing objectives and overcomes the various shortcomings of the prior art set forth above.